The present invention relates to an electroluminescent device and an electronic apparatus.
Recently, in an electronic apparatus such as a notebook computer, a portable phone, and an electronic organizer, an electroluminescent device having a plurality of electroluminescence (hereinafter, referred to as EL) elements as a unit for displaying information has been suggested. In the EL element, an EL layer (light-emitting layer) is disposed between a pair of counter electrodes.
In a field of an EL device, techniques have been known in which a specific wavelength of light is made to resonate using a multi-layered film formed by alternately laminating layers having different refractive indexes. For example, in Japanese Patent No. 2797883, an EL device is disclosed which includes a semitransparent reflective film formed of a dielectric material on the entire surface of a glass substrate, a spacer formed of SiO2 thereon, a transparent anode formed thereon, a hole injection layer formed thereon, a light-emitting layer formed thereon, and a cathode formed thereon. Although the light-emitting layer is formed of a common material in all pixels and emits white light, by varying a product of optical distances among the transparent anode, the hole injection layer, and the light-emitting layer or by varying a thickness of the spacer made of SiO2, desired output color can be obtained. Accordingly, although the light-emitting layer is formed of the same white luminescence material, the output colors of R (Red), G (Green), and B (Blue) can be obtained.
Furthermore, in JP-T-2003-528421, an EL device is disclosed which includes light-emitting layers which are formed of different materials in R, G, and B pixels, respectively, and a group of semitransparent reflective layers which overlap the light-emitting layers. The group of the semitransparent reflective layers has the same structure with regard to all the light-emitting layers, but includes a semi-reflective layer suitable for resonance of R light, a semi-reflective layer suitable for resonance of G light, and a semi-reflective layer suitable for resonance of B light, in order to improve color purity of the output light. Each of the semi-reflective layers has a plurality of low refractive-index layers (for example, a layer made of SiO2) and a plurality of high refractive-index layers (for example, a layer made of TiO2), which are alternately laminated. In each of the semi-reflective layers, the refractive index n1 and the thickness d1 of the high refractive-index layer and the refractive index n2 and the thickness d2 of the low refractive-index layer are set to satisfy a relationship of Equation 1.n1·d1=n2·d2=(¼+m/2)·λ  (1)
Here, λ is a wavelength of the light which reflects and resonates, and m is an integer more than 0. Accordingly, in each of the semi-reflective layers, the low refractive-index layers have the same thicknesses d2 and the high refractive-index layers have the same thickness d1.
However, in the EL device of Japanese Patent No. 2797883, although light of different colors can be output from white light-emitting layers, it is difficult to improve the purity of the output light. In addition, in the wavelength ranges of R, G, and B, the white luminescence material having some luminescence intensity is limited.
In addition, in the EL device of JP-T-2003-528421, actually, for example, red light of R pixel is significantly reflected from layers suitable for green light or blue light. Accordingly, light of any color pixel is significantly attenuated while passing through the group of semi-transparent reflective layers and thus desired resonance effect cannot be obtained. Further, since the light generated in the light-emitting layer reflects from and transmits various interfaces to move in various paths until being output, the excellent effect may not be obtained although the thicknesses of the low refractive-index layers and the high refractive-index layers are determined based on Equation 1. In addition, since the group of semi-transparent reflective layers includes the semi-reflective layer suitable for resonance of R light, the semi-reflective layer suitable for resonance of G light, and the semi-reflective layer suitable for resonance of B light, the number of the layers necessarily increases and thus it is difficult to manufacture the group of semi-transparent reflective layers.